Asphalts are of great utility in preparing roofing materials and the like for use in the construction and housing industries. They also find widespread use in paving materials for highways, parking lots, airports, and the like.
In many of the above applications it is often desirable to add rubbery polymers (elastomers) to the asphalt compositions. This practice, which has been known for many years, is generally done to broaden the useful temperature range of said asphalt composition by improving the ductility at low temperatures and improving the resistance to flow at elevated temperatures. It is further known that thermoplastic elastomeric block polymers of conjugated dienes and vinyl aromatic compounds are especially useful for the purposes noted above as disclosed in U.S. Pat. No. 4,196,115.
In the preparation and/or application of essentially all of the asphalt containing materials noted above, whether or not an elastomer is added, it is necessary to heat the asphalt to provide a fluid or flowable state at some point in the process. In some applications it is necessary to maintain the asphalt or asphalt-containing material at this heated fluid state for extended periods of time. In the case of paving applications, unavoidable delays due to bad weather or other factors may require the asphalt to be kept at the heated fluid state for several days. Furthermore, when an elastomer is added to the asphalt it is common practice to use heat and high shear mixing conditions to provide a good dispersion of the rubber in the asphalt and the resulting composition may have to be kept stirred while hot for extended periods of time. A serious problem has been found to occur with certain asphalts when these asphalts are subjected to the extended heating conditions described above. Said asphalts or materials containing said asphalts often undergo a sudden rapid increase in viscosity which may render them completely useless or at least greatly increase the difficulty in handling them for further use. The presence of elastomers in these asphalts seems to aggravate the problem described above. Furthermore, it has not been practical to define the limits of time and temperature through which each of these asphalts may be safely held before the onset of rapid viscosity increase. In addition, it does not appear possible at the present time to clearly identify those asphalts which will be susceptible to the problem of sudden viscosity increase without actually subjecting a sample of the asphalt or asphalt-containing composition to prolonged heating preferably under mild agitation.
It is clear that a solution to the problem of sudden viscosity increase for those asphalts which exhibit this behavior would be welcome.
The instant invention provides certain additives which minimize or eliminate the viscosity increase for the neat asphalts which are susceptible. Within the group of said additives are other additives which minimize or delay the viscosity increase for the susceptible asphalts which also contain elastomers.